university police officers sean collier was ambushed in his patrol car and killed. at 11:30 boston time, police say the brothers carjacked a man a few blocks away in cambridge. they told the driver they were the marathon bombers. a half hour later they release it had man unharmed at a gas station where a surveillance camera captured this image of sovk sok. police caught up around 1:00 a.m. then running gun battle, explosives thrown from the car. >> they have explosives, some type of grenades. they're in between houses down here. >> then it got worse. police say tamerlan approached them with a pressure cooker bomb, but it malfunctioned. >> loud explosion sfwlchlt loud explosion sfwlchlt loud explosion! . >> in all, more than 200 rounds of ammunition were exchanged. officer richard donahue was shot and critically wounded, tamerlan tsarnaev dead. in the chaos of it all, dzhokhar rather than over his older brother's body as he sped away. at 4:30 a.m. people in eastern watertown were ordered to stay in their homes. by 58 a.m., the order expanded to include all of boston.